Staying in Touch with Emerging Needs

4 weeks ago

The rising demand for better
touchscreens means consumers will increasingly expect more performance at a
lower cost. Today’s touchscreens should be thin, light, visible in varying
ambient light conditions, highly responsive and, most importantly affordable.
Quick response, transparent touchscreens are now critical to a great user
experience and can only be achieved through transparent conductors invisible to
the naked eye. A key component behind these innovative technologies is silver
nanowires.

Pro-Cap: Popular for Now

The most popular touchscreen
technology is projected capacitance or pro-cap. At the core of this technology
is a transparent conductor, a layer of material that needs to conduct
electricity. Yet it must remain transparent and allow light from the underlying
display to shine through the screen. Today’s touchscreens must be highly
responsive, bright and visible in varying ambient light conditions. This calls
for highly conductive transparent conductors with high transmission. But
pro-cap technology won’t recognize touch from a thick-gloved hand and it won’t
work with all types of stylus or a prosthetic hand.

Inherent Versatility of Transparent
Conductors

Transparent conductors can also be
used as electrodes for LCD, OLED, thin film photovoltaic cells, shutters for 3D
TVs and a whole host of applications. In general, the requirements are the same
– higher conductivity, better light transmission, and no side effects like
moiré or pattern visibility. Add to this the ability to flex a hundred thousand
times to support flexible touch screens and one begins to see the inherent
versatility of transparent conductors. The industry, of course, wants all of
this at a cost lower than today’s incumbent traditional technology. So what are
the distinctive benefits of silver nanowires for various types of touchscreen
applications?

Silver Nanowires: The New ‘Gold’
Standard

Silver nanowires are expected to
become the new gold standard in touchscreen displays, delivering a bounty of
benefits at reduced cost. The wires are usually developed and suspended in a
fluid. The resultant ink is used to coat roll-to-roll plastic film substrates
to create transparent conductive films of varying sheet resistances. Silver
nanowires can also be coated on glass or other substrates but roll-to-roll film
is most popular. The nanowires are a few tens of nanometers in diameter and a
few tens of micrometers in length. When coated on a plastic substrate (usually
PET), these high-aspect-ratio (1,000:1) silver nanowires, overlap to create a
highly conductive, yet transparent network. See Figure 1. This relatively
sparse network of high aspect ratio silver nanowires allows light to pass
through with high transmission rates. State of the art conductive films using
silver nanowires now have less than 0.2% delta haze, which is as good or better
than ITO.

Figure 1 : Silver Nanowires under
microscope, photo courtesy C3Nano

Meeting Touchscreen Requirements

Sheet resistance requirements for
transparent conductors vary by application and touchscreen size. The
conductivity requirements for a 30-inch monitor are significantly higher than
that of a touchscreen used in a four-inch mobile phone. Touchscreen applications
require highly transmissive materials for clear visibility; excellent
conductivity to ensure fast touch response: and thin, light materials for
sleek, aesthetically pleasing end products, all at a low cost. These
requirements are constantly evolving.

Today, device makers are looking for
conductivity below 70W/sq to
make their touchscreens more responsive and further improve the user
experience. For large area touchscreens in devices, such as 30-inch monitors or
42” electronic writing boards, higher conductivity is essential for a fast
response time with the ability to detect 10-finger touch. For mobile devices
like laptops and smartphones, film-based transparent conductors are in demand
to create thinner, lighter and stronger touchscreens. With flexible displays on
the horizon, transparent conductors will need the ability to be bent or rolled.
Most importantly, transparent conductor prices must be low enough to encourage
mass production of touch-enabled consumer electronic devices.

Transmission vs. Conductivity

High transmission (greater than 90
percent) along with low resistance (20 to 70W/sq) allows for 10-finger touch—the key to a great user
experience. This is particularly true for laptops, All-In-One (AIO) computers,
and other large-area capacitive touchscreens. Higher transmission also improves
battery life per charge in mobile devices and creates brighter displays since
the touch sensor does not impede light as much.

For sheet resistances of less than
130W/sq, traditional transparent conductors
like ITO are only available on glass as their annealing temperature is too high
and will damage plastic substrates. Higher conductivity with traditional
methods is obtained by depositing a thicker layer of transparent conductor on a
glass substrate, which takes more time to deposit, thus reducing throughput.

In contrast, silver nanowire ink can
be coated at around 100° C—much
lower than the softening temperatures of plastic films. Mass production
throughput is also consistently high, regardless of sheet resistance
requirements. For lower sheet resistance, product designers need only apply a
thicker coating of silver nanowire ink at the same coating speed (hence same
throughput).

Pattern Visibility and Moiré

Moiré effect occurs when the eye sees
a set of lines or dots over another set of lines or dots. This visual image can
considerably degrade the quality and resolution of images, particularly on a
touchscreen. Silver nanowires have no moiré issues and almost no pattern
visibility due to the random distribution of the nanowires.

ITO is usually deposited on glass,
resulting in a fragile, heavy glass touch sensor that is about 0.7 – 1.5 mm
thick. In comparison, a silver nanowire film-based touch sensor is only 0.2 –
0.4mm thick. Silver nanowire sensors on film are roughly 45 percent lighter and
50 percent thinner than its ITO counterpart, giving film-based silver nanowire
sensors a big advantage.

Flexible, Wearable Displays And
Touchscreens

Necessity being the mother of
invention, it didn’t take long for display manufacturers to realize that too
many mobile phone users were sitting on and cracking their touchscreens.
Result: touchscreens are becoming increasingly flexible. In fact, touchscreens
have become so flexible that you may soon be able to fold or roll up your
smartphone or tablet when not in use. See Figure 2.

Flexibility is clearly the next big
trend in touchscreens and displays, allowing for enhanced portability,
durability, and unique designs. Imagine unbreakable phone screens that would
flex instead of shattering when dropped, the ability to fold your seven-inch
tablet so that it fits in your pocket, or displays that wrap around your arm, a
pillar or building. Products like these are slowly becoming a reality and are driving
demand for flexible, bendable and rollable touchscreens.

Figure 2 : Flexible touchscreen,
photo courtesy, C3Nano

Touchscreens Ideal for Large Area
Displays

Often seen in corporate meeting
rooms, executive or customer briefing areas, huddle spaces, and
college/universities, large touch screen based devices have become increasingly
popular. They are popular as Ideation platforms, they make for great electronic
writing, sharing, real-time collaboration and offer better security than the
traditional white board where someone takes a picture before it is erased. See
figure 3. In these types of devices, there is a need for highly transparent and
highly conductive touch sensors and silver nanowires play an enabling role in
such applications.

Automotive manufacturers are
integrating touchscreens into center stack displays, navigation systems,
human-machine interfaces (HMIs), keyless entry, and rear-seat entertainment
systems. According to a recent study, shipments of touchscreen displays
for automotive applications rose sharply in 2018. This trend is expected to
increase over the next four years, with projected shipments exceeding 65
million units in 2021.

Conclusion

For emerging touchscreen
applications, including large area touchscreens, as well as flexible display
applications, silver nanowires offer a significant advantage, both in cost and
performance. Currently used in several consumer products, silver nanowire
material offers lower manufacturing and per-unit costs and makes scaling much
easier. Roll-to-roll processed silver nanowire transparent conductors are the
clear choice for new production facilities that need high throughput and easy
processing, as well as for device manufacturers that need a thin, light,
flexible material to deliver high performance for innovative devices.